FIELD OF THE INVENTION
The invention relates to a suction gripper in a reversing device of a sheet-fed rotary printing machine, the suction gripper, in order to take over a trailing edge of a sheet conveyed on an upline sheet-conveying cylinder, being movable out of a periphery of a downline sheet-conveying cylinder, gripping the sheet to be reversed in a region of the trailing edge thereof, and moving back in a substantially radial direction towards the downline sheet-conveying cylinder, at which the trailing edge of the sheet is transferable to a further gripper device.
The German Published Non-prosecuted Patent Application (DT-OS) 38 29 626 discloses a sheet-fed rotary printing machine having a reversing device in which, during perfecter printing, a suction gripper is pivoted out of the periphery of a cylinder disposed downline from an impression cylinder, and towards the circumferential surface of the impression cylinder, at which it grips the trailing edge of a sheet to be reversed and, before the suction gripper passes the gripper center line between the two cylinders, it transfers this trailing edge into the periphery of the downline cylinder. In the described device, no axial smoothing of the sheets takes place after the transfer by the suction gripper and, because of the rigid and stiff configuration of the suction gripper and of the permanently predefined pivoting travel, widely varying contact forces, possibly leading to register errors, result during the processing of printing materials of different thicknesses.
The published European Patent Document EP 0 649 742 A1 discloses a further generic reversing device, in which the suction grippers which take over the trailing edge are formed as rotary suckers which, because of the configuration and weight thereof, cannot be moved out of the periphery of the downline cylinder, however, or can be moved out only with a great amount of engineering effort. As a result, particularly at the continuous printing speeds which are presently common during perfecter printing, transfer problems may occur, and these have a detrimental effect upon in-register transfer.
Furthermore, the German Patent 30 36 790 discloses a reversing device that operates on the three-drum reversing principle and has a storage drum in which suction grippers, which are arranged within the periphery of the storage drum and which hold on the storage drum the trailing edge of the sheet to be reversed, are displaceable in the axial direction along a guide rod in order to smooth the sheet trailing edge axially before it is transferred to the downline reversing drum. Because of the different reversing principle, in the case of the described device there is no axial tautening of the sheets during the transfer of the sheet trailing edge, and the suction grippers, because of the comparatively complicated mechanical configuration thereof and the fact that they are guided within the periphery of the storage drum, are comparatively heavy and cannot be moved out of the latter.